A large number of degenerative eye disorders, such as glaucoma and macular degeneration, may be detected by evaluating a subject's visual field, such as through visual field perimetry. In visual field perimetry, a subject's eye is typically fixated on a stationary target (a “fixation point”) while visual test stimuli are displayed momentarily within the subject's visual field. The subject's visual field is then mapped by recording his/her response to each visual test stimulus. To reduce eye fatigue, however, various methods have been developed which use instead a moving fixation point. With respect to such a moving fixation point, selected patents as discussed herein below are of interest, and are incorporated herein by reference.
In U.S. Pat. No. 4,995,717, a fixation point is moved around a computer screen while the subject attempts to track its movement by means of a computer mouse. More particularly, the subject moves the cursor, such as a circle, by means of the mouse to keep the fixation point surrounded by the cursor. Fixation is maintained while the cursor is surrounding the fixation point, allowing test stimuli to then be displayed within the subject's peripheral vision.
In U.S. Pat. No. 5,565,949, a fixation point again is moved around a computer screen, but during its movement it changes shape, for example, from a circle to a square, or vice a versa. After such a change in the fixation point, the subject is required to press a mouse button. Failure to respond to the change indicates a loss of fixation.
In U.S. Pat. No. 5,737,060, a moving fixation point, such as in the shape of an ant, is displayed on two independent screens of virtual reality glasses, which are worn by the subject. The fixation point is moved around the display screen of the glasses, with its overall direction of movement being clockwise. Two methods of monitoring fixation are used. In one, the subject must respond to changes in the direction of the fixation point though the use of a computer mouse. Any change in direction which the subject does not respond to is considered a loss of fixation. In the second method, blindspot monitoring is used as the fixation control. In this latter case, a target is displayed in the subject's blindspot on one of the display screens, while the fixation point is displayed on the other screen. If the subject responds to the blindspot target, then there is a loss of fixation since the blindspot target should not have been seen. Otherwise, it is assumed that fixation has been maintained.
Although computerized visual field perimetry systems satisfactorily employ fixation methods, whether stationary or moving, as discussed above herein, it would be desirable to have a method and system for establishing fixation which is less complicated, and can function using speech recognition as the method of input for the entire test. Morever, may fixation methods typically require costly equipment, such as the use of video cameras and eye tracking instruments. As such, it would be further desirable to have a method and system for establishing fixation which is less costly.